The present invention relates to a hot-melt transfer ink image-receiving sheet that has excellent abrasion resistance, is useful as a contact printing film using a photomechanical process and achieves excellent image density and halftone dot reproducibility in a recorded image.
Thermographic recording methods, which do not require post-processing such as development and fixation unlike the silver salt photographic recording method and the electrophotographic recording method, have been employed as a method for making various hard copies which does not produce processing wastes. The thermographic recording methods include a direct thermographic method, wherein a thermal color developing layer obtained by dispersing a color precursor, color developer, sensitizer and so forth in a binder resin is provided on an image-receiving sheet and the thermal color developing layer is heated to develop color, and a hot-melt transfer method, wherein a hot-melt transfer ink layer of an ink ribbon is transferred on an image-receiving sheet.
When a contact printing film using a photomechanical process is prepared by the direct thermographic method, small characters and minute halftone dots can be reproduced and hence a high-resolution image can be obtained. However, image density enough to print a photographic material cannot be obtained, and thus there was a difficulty to use this method in practice.
On the other hand, when a contact printing film in the photomechanical process is prepared by the hot-melt transfer method, image density enough to print a photographic material can be obtained when high light-shielding property is imparted by making a hot-melt transfer ink layer of the ink ribbon thick. However, when an ink ribbon having a thick hot-melt transfer ink layer is used to record an image on a conventional known image-receiving sheet such as a transparent plastic film, small characters and minute halftone dots cannot be reproduced due to insufficient fixation property of the transferred image on an image-receiving sheet and ununiform transfer.
In order to solve these problems, an ink ribbon which has a thin hot-melt transfer ink layer and high light-shielding property needs to be used. However, when an image is recorded on a conventional known image-receiving sheet such as a transparent plastic film, the transferred image could not be imparted with sufficient image density and abrasion resistance.
In order to impart abrasion resistance to an image, a method is considered wherein the image-receiving surface of the hot-melt transfer ink image-receiving sheet is roughened so that hot-melt transfer ink should be buried in the image-receiving sheet to improve fixation property for the ink. However, while the abrasion resistance is improved when the image-receiving surface is roughened, protruding portions of the image-receiving surface penetrate the hot-melt transfer ink, which results in occurrence of pinholes. The occurrence of pinholes degrades image density and prevents formation of high-quality halftone dots and thus a problem arises that reproducibility of halftone dots is degraded in the photomechanical process. This problem is particularly noticeable when an ink ribbon which has a thin ink layer and high light-shielding property is used to reproduce minute halftone dots as described above.
On the other hand, occurrence of pinholes can be prevented by reducing the roughness of the image-receiving surface. However, this results in insufficient fixation property for the hot-melt transfer ink and thereby degrades abrasion resistance of an image. Further, in this case, a so-called reverse transfer, wherein an image transferred onto the image-receiving surface is reversely transferred to an overlapped ink ribbon, occurs and hence a part of the image is deleted. Thus, the halftone dot reproducibility is further degraded.
Accordingly, an object of the present invention is to provide a hot-melt transfer ink image-receiving sheet that is excellent in image abrasion resistance as well as halftone dot reproducibility and image density even when an ink ribbon having a thin hot-melt transfer ink layer is used, and is useful as a contact printing film in a photomechanical process.
The inventors of the present invention have found that, while image abrasion resistance correlates with arithmetic mean deviation Ra of surface roughness (JIS-B0601), the levels of the image density and halftone dot reproducibility, while not necessarily reflected in arithmetic mean deviation Ra, correlate with 10-point height of irregularities Rz. They further found that excellent abrasion resistance as well as favorable image density and halftone dot reproducibility could be obtained by defining both Ra and Rz within predetermined ranges.
Specifically, the hot-melt transfer ink image-receiving sheet of the present invention is a hot-melt transfer ink image-receiving sheet having an image-receiving surface on a support, wherein the image-receiving surface has surface roughness (JIS-B0601) of 0.15-0.60 xcexcm in terms of arithmetic mean deviation Ra and 1.0-2.5 xcexcm in terms of 10-point height of irregularities Rz.
Preferably, the image-receiving surface consists of an overcoat layer containing an emulsion resin of which glass transfer temperature is 50-120xc2x0 C. Examples of the emulsion resin include a homopolymer and copolymer of monomer selected from ethylene, styrene, vinyl chloride, vinyl acetate, acrylonitrile, methyl methacrylate.
The hot-melt transfer ink image-receiving sheet of the present invention may have an image-receptive layer comprising a binder resin and a surface-roughening agent formed on the support. Preferably, the surface-roughening agent is amorphous silica and has an average particle diameter in the range of 1.0-5.0 xcexcm.
It is also preferable that the hot-melt transfer ink image-receiving sheet has ultraviolet ray transimissivity of lower than 0.3 in terms of ultraviolet ray transmission density.